Chondroitin sulfate, which is a kind of glycosaminoglycan (GAG), exists as a proteoglycan on cell surfaces and in an extra cellularmatrix, Chondroitin sulfate draws attendtion because Chondroitin sulfate plays an important role in neural network formation in the developing mammalian brain (Arch. Biochem. Biophys. 374, 24-34 (2000); Trends Glycosci, Glycothenol. 12 321-349 (2000).
Chondroitin sulfate has a straight-chained polymer structure having a repeating disaccharide unit having a glucuronic acid residue (GlcUA) and an N-acetylgalactosamine residue (GalNAc). A serine residue in a core protein is covalent-bonded with chondroitin sulfate via 4-saccharide structure (GlcUAβ1-3Galβ1-3Galβ1-4Xylβ1) peculiar thereto (Glycoproteins, ed. Gottsthalk, A. (Elsevier Science, New York), pp. 491-517 (1972); The Biochemistry of Glycoproteins and Proteoglycans; ed. Lennarz, W. J. (Plenum, New York), pp. 267-371 (1980)).
GAG is biosynthesized by sequentially transferring saccharides from UDP-sugar to a non-reducing end of a saccharide chain. It was found that (a) purification of bovine serum gave a glycosyltransferase that involves in biosynthesis of a repeating disaccharide unit of heparin/heparan sulfate, and (b) cDNA cloning revealed that a single protein of the glycosyltransferase catalyses both transferase reactions of N-acetylglucosamine residue (GlcNAc) and GlcUA.
On the other hand, a glycosyltransferase that involved in biosynthesis of the repeating disaccharide unit of chondroitin sulfate has not been cloned yet except the chondroitin synthase derived from a bacterium (J. Biol. Chem. 275, 24124-24129 (2000)). GlcUA transferase II (GlcAT-II) and GalNAc transferase II (GalNAcT-II) have been purified from avian cartilage (J. Biol. Chem. 272, 14399-14403 (1997)) and from bovine serum (Eur. J. Biochem. 264, 461-467 (1999)). However, cDNA cloning of those enzymes has not been performed yet because it is difficult to purify those enzymes to form homogeneity.
An object of the present invention is to provide (a) a vector having DNA encoding human chondroitin synthase, (b) a method of producing human chondroitin synthase, (c) a method of producing a saccharide chain having a repeating disaccharide unit of chondroitin, and (d) a probe for hybridization of human chondroitin synthase.